[mojo] Add CreateSharedBuffer method to Broker.

mojo/edk/system/child_broker.cc

Index: mojo/edk/system/child_broker.cc
diff --git a/mojo/edk/system/child_broker.cc b/mojo/edk/system/child_broker.cc
index 6903c8204dbd23b393729c8e859407609dc983db..627e1eb23b3ddac526ad1d3e599ed04b26007223 100644
--- a/mojo/edk/system/child_broker.cc
+++ b/mojo/edk/system/child_broker.cc
@@ -13,9 +13,17 @@
 #include "base/logging.h"
 #include "mojo/edk/embedder/embedder_internal.h"
 #include "mojo/edk/embedder/platform_channel_pair.h"
+#include "mojo/edk/embedder/platform_shared_buffer.h"
+#include "mojo/edk/embedder/platform_support.h"
 #include "mojo/edk/system/broker_messages.h"
 #include "mojo/edk/system/message_pipe_dispatcher.h"
 
+#if defined(OS_POSIX)
+#include <fcntl.h>
+
+#include "mojo/edk/embedder/platform_channel_utils_posix.h"
+#endif
+
 namespace mojo {
 namespace edk {
 
@@ -26,24 +34,34 @@ ChildBroker* ChildBroker::GetInstance() {
 
 void ChildBroker::SetChildBrokerHostHandle(ScopedPlatformHandle handle)  {
   ScopedPlatformHandle parent_async_channel_handle;
+  parent_sync_channel_ = std::move(handle);
+
+// We have two pipes to the parent. The first is for the token
+// exchange for creating and passing handles on Windows, and creating shared
+// buffers on POSIX, since the child needs the parent's help if it is
+// sandboxed. The second is used for multiplexing related messages. We
+// send the second over the first.
 #if defined(OS_POSIX)
-  parent_async_channel_handle = std::move(handle);
+  // Make the synchronous channel blocking.
+  fcntl(parent_sync_channel_.get().handle, F_SETFL,

[Anand Mistry (off Chromium), 2016/01/07 04:36:33]

Since you rely on the channels becoming blocking, I think these calls to fcntl()
should check the return value using PCHECK.

[Eliot Courtney, 2016/01/07 05:01:30]

Done.

+        fcntl(parent_sync_channel_.get().handle, F_GETFL, 0) & ~O_NONBLOCK);
+
+  std::deque<PlatformHandle> received_handles;
+  char buf[1];
+  ssize_t result = PlatformChannelRecvmsg(parent_sync_channel_.get(), buf, 1,
+                                          &received_handles);
+  CHECK_EQ(1, result);
+  CHECK_EQ(1u, received_handles.size());
+  parent_async_channel_handle.reset(received_handles.front());
 #else
-  // On Windows we have two pipes to the parent. The first is for the token
-  // exchange for creating and passing handles, since the child needs the
-  // parent's help if it is sandboxed. The second is the same as POSIX, which is
-  // used for multiplexing related messages. So on Windows, we send the second
-  // pipe as the first string over the first one.
-  parent_sync_channel_ = handle.Pass();
-
   HANDLE parent_handle = INVALID_HANDLE_VALUE;
   DWORD bytes_read = 0;
   BOOL rv = ReadFile(parent_sync_channel_.get().handle, &parent_handle,
                      sizeof(parent_handle), &bytes_read, NULL);
   CHECK(rv);
   parent_async_channel_handle.reset(PlatformHandle(parent_handle));
-  sync_channel_lock_.Unlock();
 #endif
+  sync_channel_lock_.Unlock();
 
   internal::g_io_thread_task_runner->PostTask(
       FROM_HERE,
@@ -99,6 +117,30 @@ void ChildBroker::TokenToHandle(const uint64_t* tokens,
     sync_channel_lock_.Unlock();
   }
 }
+#else
+scoped_refptr<PlatformSharedBuffer> ChildBroker::CreateSharedBuffer(
+    size_t num_bytes) {
+  sync_channel_lock_.Lock();

[Anand Mistry (off Chromium), 2016/01/07 04:36:33]

Why aren't you using AutoLock?

[Eliot Courtney, 2016/01/07 05:01:30]

This lock is actually a LockImpl, see comment:
https://code.google.com/p/chromium/codesearch#chromium/src/mojo/edk/system/ch...

As far as I can tell you can't use AutoLock with it.

+  scoped_refptr<PlatformSharedBuffer> shared_buffer;
+
+  BrokerMessage message;
+  message.size = kBrokerMessageHeaderSize + sizeof(uint32_t);
+  message.id = CREATE_SHARED_BUFFER;
+  message.num_bytes = num_bytes;
+
+  std::deque<PlatformHandle> handles;
+  if (WriteAndReadHandles(&message, &handles)) {
+    DCHECK_EQ(1u, handles.size());
+    PlatformHandle handle = handles.front();
+    if (handle.is_valid())
+      shared_buffer =
+          internal::g_platform_support->CreateSharedBufferFromHandle(
+              num_bytes, ScopedPlatformHandle(handles.front()));
+  }
+
+  sync_channel_lock_.Unlock();
+  return shared_buffer;
+}
 #endif
 
 void ChildBroker::ConnectMessagePipe(uint64_t pipe_id,
@@ -172,10 +214,8 @@ ChildBroker::ChildBroker()
       in_process_pipes_channel2_(nullptr) {
   DCHECK(!internal::g_broker);
   internal::g_broker = this;
-#if defined(OS_WIN)
   // Block any threads from calling this until we have a pipe to the parent.
   sync_channel_lock_.Lock();
-#endif
 }
 
 ChildBroker::~ChildBroker() {
@@ -285,6 +325,21 @@ void ChildBroker::AttachMessagePipe(MessagePipeDispatcher* message_pipe,
 
 #if defined(OS_WIN)
 
+void ChildBroker::CreatePlatformChannelPairNoLock(
+    ScopedPlatformHandle* server,
+    ScopedPlatformHandle* client) {
+  BrokerMessage message;
+  message.size = kBrokerMessageHeaderSize;
+  message.id = CREATE_PLATFORM_CHANNEL_PAIR;
+
+  uint32_t response_size = 2 * sizeof(HANDLE);
+  HANDLE handles[2];
+  if (WriteAndReadResponse(&message, handles, response_size)) {
+    server->reset(PlatformHandle(handles[0]));
+    client->reset(PlatformHandle(handles[1]));
+  }
+}
+
 bool ChildBroker::WriteAndReadResponse(BrokerMessage* message,
                                        void* response,
                                        uint32_t response_size) {
@@ -316,21 +371,38 @@ bool ChildBroker::WriteAndReadResponse(BrokerMessage* message,
 
   return result;
 }
+#else
+bool ChildBroker::WriteAndReadHandles(BrokerMessage* message,
+                                      std::deque<PlatformHandle>* handles) {
+  DCHECK_EQ(0,
+            fcntl(parent_sync_channel_.get().handle, F_GETFL, 0) & O_NONBLOCK);
+  CHECK(parent_sync_channel_.is_valid());
 
-void ChildBroker::CreatePlatformChannelPairNoLock(
-    ScopedPlatformHandle* server, ScopedPlatformHandle* client) {
-  BrokerMessage message;
-  message.size = kBrokerMessageHeaderSize;
-  message.id = CREATE_PLATFORM_CHANNEL_PAIR;
-
-  uint32_t response_size = 2 * sizeof(HANDLE);
-  HANDLE handles[2];
-  if (WriteAndReadResponse(&message, handles, response_size)) {
-    server->reset(PlatformHandle(handles[0]));
-    client->reset(PlatformHandle(handles[1]));
+  uint32_t remaining_bytes = message->size;
+  while (remaining_bytes > 0) {
+    ssize_t bytes_written = PlatformChannelWrite(
+        parent_sync_channel_.get(),
+        reinterpret_cast<uint8_t*>(message) + (message->size - remaining_bytes),
+        remaining_bytes);
+
+    if (bytes_written != -1)
+      remaining_bytes -= bytes_written;
+    else
+      return false;
   }
-}
 
+  // Perform a blocking read (we set this fd to be blocking in
+  // SetChildBrokerHostHandle).
+  char buf[1];
+  ssize_t bytes_read =
+      PlatformChannelRecvmsg(parent_sync_channel_.get(), buf, 1, handles);
+  // If the other side shutdown, or there was an error, or we didn't get
+  // any handles.
+  if (bytes_read == 0 || bytes_read == -1 || handles->empty())
+    return false;
+
+  return true;
+}
 #endif
 
 }  // namespace edk